In recent years, wireless LANs (Local Area Networks) have rapidly become popular. Standards of wireless LANs include, for example, IEEE (Institute of Electrical and Electronic Engineers) 802.11a using a 5.2 GHz bandwidth, and IEEE 802.11g using a 2.4 GHz bandwidth. In IEEE 802.11a and IEEE 802.11g, communication is performed with use of a multicarrier communication method called OFDM (Orthogonal Frequency Division Multiplexing).
The following describes an overview of processing for detecting the packet signal performed by a signal detection device provided in a receiver, when using the wireless LAN communication method that uses OFDM.
The transmitter adds a repeating signal, which is a training symbol repeated a plurality of times, to the head of the packet signal, and transmits the packet signal to the receiver. The training symbol is a symbol whose signal waveform has a predetermined pattern. Note that if the targeted wireless LAN uses, for example, the IEEE 802.11a standard, the training symbol is called a short training symbol.
The signal detection device sequentially obtains correlation values that correlate a reception signal with a pre-stored reference signal. The signal detection device compares each of the correlation values to a threshold determined according to a power level of the received signal, and detects positions on a time axis corresponding to correlation values that exceed the threshold. If a series of time intervals between adjacent detected positions is a repeating cycle of the training symbols, the signal detection device judges that the packet signal has arrived, and estimates a symbol timing as a reference for demodulating the packet signal (for example, see patent document 1).
Note that the reference signal used in conventional technology is the same signal as the signal waveform of the training symbol at the time that the training symbol was added to the head of the packet signal by the transmitter.
Patent document 1: Japanese Patent Application Publication No. 2001-127745